Spark device



United tates Patent() SPARK DEVICE Louis H. Segall, Sidney, N. Y., assignor to Bendix Aviation Corporation, Sidney, N. Y., a corporation of Delaware Application February 7, 1957, Serial No. 638,761 18 Claims. (Cl. 313-130) This invention relates to electrical apparatus and more prticularly to spark gaps for ignition circuits and the li e.

One of the objects .of the present invention is to provide a-spark gap device of novel and simplified construction.

Another object of the invention is to provide a novel spark gap which has a very narrow constricted gap and which is highly eflicient in the conversion of`electrical energy into heatenergy in the form of a spark or an arc.

A further object is to provide a novel apparatus for producing electrical sparks which is so constructed that the cooperating electrodes are definitely and accurately spaced by insulators which cooperate to form the constrained gap of the device.

AStill another object is to provide a novel sparking device having a constrained or constricted gap, the device being of such construction that the constricted passage-forming surfaces interposed between the electrodes of the gap may readily be provided with the desired surface charac.-v

teristics.

The above and further objects and novel features ofthe present invention will more fully appear from the following detailed description when the same is read in 'connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for purposes of illustration only and are not intended as a definition of the limits of the invention.

In the drawings:

Fig. 1 is an enlarged fragmentary longitudinal sectional view of one form of spark gap device embodying the invention, certain of the parts being shown in elevation;

Fig. 2 is a bottom view of the device of Fig. l;

Fig. 3 is an enlarged View in section through a portion of theinterface between the inner and outer insulators forming the constricted passage between the electrodes lof the constrained gap of the device of Fig. 1; Fig. 4 is a View in section, similar to Fig. 3, of a modication of the constrained gap shown in Figs. 1, 2, and 3; Fig. 5 is an enlarged fragmentary longitudinal sectional view of a second form of spark gap device in accordance with the invention;

Fig. 6 is a bottom view of the device of Fig. 5;

Fig. 7 is a view in axial section through a modiied outer constricted passage-forming insulator for `a device such as shown in Fig. 5; and,

Fig. 8 is a fragmentary view in isometric projection of a modified inner constricted passage-forming insulator for a spark gap device such as that shown in Fig. 5.

The several embodiments of the invention illustrated in the drawings, by way of example, and the modifications thereof described below, are in the form of tip or electrode assemblies adapted for use in spark or igniter plugs of the type disclosed in copending application Serial No. 221,435, tiled April 17, 1951 now Patent No. 2,786,158, March 19, 1957. Structures of this type are particularly adapted for use in ignition systems 'of combustion engines wherein it is advantageous to have a conice l`2 centrated hot spark projected into lthe combustible charge. In the embodiment shown in AFigs. 1 to 4, inclusive, a tubular metalshell 10 has an internal ange 11 at one end, the flange supporting a central electrode` assembly and also serving as one of the gap electrodes. Shell 10 is usually grounded to an engine casing or other structure which serves as a connection to one terminal of a source of electrical energy. ln the specific form shown, iiange 11 has a central circular 'hole or passage therethrough, the inner edge 12 of the flange at such passage functioning as the primarily activated surface of the outer electrode.

Flange 11 also functions as an end support for an internal assembly including an inner electrode and two insulators which cooperate to space 'the two electrodes of the spark gap device` and to present between them an an# nular constricted passage interposed between the electrodes to form a constrained spark gap; The inner assembly is made up of a iirst or outer insulator 14 which, as shown, is of tubular form and is snuglyV received within shell 10. The insulator 14 has a relatively large circular cylindrical bore 22 in its inner end, the openingv through insulator 14 tapering radially inwardly from the bottom of bore 22 in the direction toward ange 11. ,In the embodiment shown, the outer, smaller diametered end of the frusto-conical portion 15 ofthe passage is smoothly curved at 21 so as to expose at least the inner edge of surface 12 of the outer electrode.

Positioned in the inner part of tapered portion 15 of the passage in insulator 14 is a frusto-conical disc-like inner electrode 16 which, in the form shown, may be an enlarged head onV a central stem or lead 17 adapted to be connected to a suitable source of high voltage current. Electrode 16 is positioned in at least substantial abutment with the larger, inner end of a'frusto-conical second insulator 20 which is positioned in the outer endof seat 15. The constricted passage 19 forming the constrained gap between electrodes 12 and 16 of a first illustrative embodiment of the device is shown in Fig. 3. In such device, insulators 14 and 20, which may be made of ceramic insulating material such as fused aluminumA or the like are both shown as having rough unpolished surfaces confronting each other. ln accordance with the invention it is suicient that only one such surface be rough. As a consequence of such roughness of one Ior both the confronting, constricted passage-forming surfaces of insulators 14 and 20, the two insulators Contact each other at random points only and present a frusto-conical annular gap between them, so `that spark discharges may take place generally throughout the extent of the gap. It will be understood that the desired effective average widthpof the constricted passage of the gap may be varied by variation in the degree of roughness of one or. both of the gap-forming surfacesjof the insulators.

Ordinarily it is preferred that the average width of the A constricted passage of the gap shall lie between .001 and .003 inch, but the average width in some instances within the scope of theinvention may be as high as .015 inch. When the passage-forming surface ,of one insulator is polished andthe other is rough, surface protuberances on the rough surface of .001 inch above the general surface will yield a passage having a width of about .001 inch.

In the device shown, the inner insulator 20 and the inner electrode 16 are retained iirmly and accurately in place by an upper insulator member 24 having a larger diametered portion 26 snugly received within the inner end of bore 2 2 in insulator4 14. Glass 27, which may be sintered in place, is interposed betweenjinsulator'24 and electrode 16, as shown, whereby 'to seal together members 14, 24, and 16. A metal retaining ring 29, pressed into shell 10, holds the 'central assembly inplace.. Thevdesribed tip may be conventionally mounted upon" a body 30 of the device as by being welded thereto along line 31.

In Fig. 4 there is shown a modification of the constrained spark gap device of Fig. l. In Fig. 4 a portion of a modified inner insulator 20 'is shown positioned within a conical seat in outer insulator 14. The peripheral surface of insulator is provided with a plurality of longitudinal extending grooves 32 (one shown) whereby to provide a spark gap having a somewhat larger effective area, at least at the grooved zones thereof, than that of Fig. 3. It will be understood that essentially the same result may be achieved by grooving the seat 15 of insulator 14. In one construction in accordance with Fig. 4, the grooves 32 are positioned 30 apart about the airis of insulator 20', and such grooves are of generally square section having a depth and width of from .005 to .015 inch. In another such construction the grooves are semicircular in section, and'have a radius of from .005 to .015 inch.

l The spark gap device of the embodiment shown in Fig. 5 includes a shell 40 having an internal flange 41 at one end thereof, the inner edge 42 of the central opening through flange 41 serving as the first electrode of the device. A first or outer insulator 43 in the form of a sleeve having an internal flange 44 at the outer end thereof is snugly received in shell 40. The inner edge of flange 44 is in the form of a shallow outwardly converging frustum 45 of a cone. The second or inner electrode 46 is formed as a circular cylindrical disc received in circular cylindrical bore 52 of insulator 43 and secured as by welding or soldering to a stem or lead 47. Positioned within seat 45, and cooperating with the flange 44 of the insulator 43 to space the two electrodes is a conical -ceramic insulator 50, the apex 53 of which projects appreciably outwardly beyond the outer electrode 42.

The described central assembly is positioned and sealed in shell 40 by an upper insulator 54 having a larger diametered portion 56 snugly received in shell 40 and a smaller diameter portion 55 received in bore 52 of insulator 43. A` glass seal 57 is interposed between members 43, 46, 54 and 47. Avretaining ring 59 overlies insulator 54, and the described tip isv shown attached to body 60 by an annular weld 61.

`It has been found that, in some instances, the conical shape of inner insulator 50 is of advantage in `aiding in the projection outwardly of the hot ionized gaseous products resulting from discharge of the device. The device of Fig. 5 may be modified, however, by cutting off the body 50 generally along the horizontal dotted line shown in Fig. 5 to form a frustum of a cone, its outer end lying flush with the inner surface of flange 41.

In some instances it is desirable to provide at least the constricted passage-forming surface of one of insulators 43 and 50 of an electrically semi-conducting material, whereby the gap operates efficiently at low voltages.

In Fig. 7 there is shown a modified first insulator 43 having a semi-conductive coating 62 overlying the conical constricted passage-forming surface thereof and also the adjacent upper and lower surfaces of flange 44. One semi-conductive coating material which has been found satisfactory is that disclosed in the application of Harris, Serial No. 600,210, filed July 26, 1956. It will be understood, however, that if desired insulator 43 may be made of ceramic material which itself is semi-conductive. One such material is that disclosed in the application of White, Serial No. 248,845, filed September 28, 1951, now Patent No.` 2,806,005, September l0, 1957, and another such material being that disclosed in the application of Harris, Serial No. 248,844, filed September 28, 1951, now abandoned.

As an alternative, the second or inner insulator 50 may be provided with an outer' coating lof semi-conducting material. In Fig. 8 an inner insulator, there designated 50,`is` shown provided with a semi-conductive coating 64 on its outer conical surface.

tion, as the same will now be understood by those skilled 1 in the art.

What is claimed is:

l. A spark gap device comprising a tubular shell having an internal flange forming a first electrode, a first, tubular insulator in said shell having an end surface engaging the inner surface of the shell flange, the first yinsulator having an opening therethrough, the end of the opening nearer the shell flange forming a seat tapered with its smallest diameter adjacent said shell flange, a second insulator` seated in such tapered portion of the opening in the first insulator, thereby forming a highly constricted annular pass/age, a second electrode in said first insulator in spark gap relation with said shell flange, said constricted annular passage being interposed between the first and second electrodes.

2. A spark gap device as defined in claim l wherein the second insulator is of such configuration as to have generally annular face-to-face contact with the seat over an appreciable distance axially ofthe seat.

3. A spark gap device as defined in claim 2 wherein at least one of the passage-defining surfaces of `the first and second insulators is provided with spaced shallow grooves extending generally longitudinally of the gap.

4. A spark gap device as defined in claim 2 wherein the seat and the second insulator are in the form of a surface of revolution land a body of revolution, respectively.

5. A spark gap device as defined in claim 4 wherein the outer end of the annular constricted gap lies somewhat radially inwardly of the radially inner edge of the shell flange.

6. A spark gap device as defined in claim 4 wherein the seat and the second insulator are tapered at substantially the same angle.

7. A spark gap device as defined in claim 6 comprising means to maintain the second electrode in contact with the second insulator, to maintain the second insulator firmly in the seatv in the first insulator, and to effect a seal between the second electrode and the second insulator.

8. A spark gap' device as defined in claim l wherein the second electrode lies in contact with the end of the second insulator remote from the first electrode.

9. A spark gap device as defined in claim 1 wherein at least one of the passage-defining surfaces of the first and second insulators is made of ceramic material and is unpolished. l

10. A spark gap device as defined in claim 1 wherein at least one of the passage-defining surfaces of the first and second insulators is made of material which-is electrically semi-conducting.

said semi-conducting material is in the form of a coating layer on its respective insulator body.

'12. A spark gap device as defined in claim ll wherein at least one of the passage-defining surfaces of the first yand second insulators is provided with spaced shallow grooves extending generally longitudinally of the gap.

13. A spark gap device comprising a tubular shell having an internal flange forming a first electrode, a first tubular insulator in said shell having an end surface engaging the inner surface of the shell flange,v the first insulator having an opening therethrough, said opening being generally cylindrical in its inner portion and tapering radially inwardly .froml the cylindrical portion at the outer end adjacent the shell flange to form a seat, a second insulator lpositioned in and closely fitting the seat to form therewith a highly constricted annular passage, a

second electrode, positioned in the tapered outer portion of the passage in the first insulator, in spark gap relation with said shell ange, said constricted annular passage being interposed between the rst and second electrodes.

14. A spark gap device as defined in claim 13 wherein the second electrode is tapered in the same direction as the second insulator and closely interlits with the tapered seat in the first insulator.

15. A spark gap device comprising a tubular shell having an internal flange forming a first electrode, a first tubular insulator in said shell having an internal flange engaging the inner surface of the shell flange, the opening through the fiange on the first insulator being tapered with its smallest diameter adjacent such shell ange to form a seat, a second insulator positioned in and closely fitting the seat to form therewith a highly constricted annular passage, a second electrode, positioned in the cylindrical outer portion of the passage in the first insulator, in spark gap relation with said shell ange, said 6 v constricfed annular passage being interposed between the first and second electrodes.

16. A spark gap device as defined in claim l5 wherein the second electrode is generally in the form of a cylindrical disc, and is positioned in the first insulator above the flange thereof and with its outer end overlying and abutting the inner end of the second insulator.

17. A sparking device comprising a pair of spaced electrodes, means including two insulators having generally face-to-face engagement separating said electrodes, the spark gap between said electrodes consisting in part of the passage between the engaging surfaces of said insulators.

18. A sparking device comprising two insulators having surfaces in generally face-to-face engagement, and a pair of electrodes in spark gap relation through the constricted passage between said engaging surfaces of the insulators.

No references cited. 

